Trayvon Martin 911 Call: How Experts ID Voices

George Zimmerman poses for a mug shot in this 2005 booking photo in Florida. Voiceprint analysts have said the voice calling for help on a 9-11 tape is not his.

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The remains of Yassir Arafat, the Palestinian leader who died in Paris in 2004, have been exhumed following allegations that the 75-year-old succumbed not to a stroke, according to hospital records, but rather was poisoned.
Arafat's death was an event "surrounded by contention and mystery," as described by the New York Times. Though results of forensic tests aren't expected for another three months, identifying the culprits if foul play were determined to be the cause of Arafat's passing will be impossible. In other words, a conclusive result might only deepen a historical mystery.
The Arafat inquiry might not yield conclusive results, but forensic scientists have proven effective at reaching hundreds of years back into history and coming back with answers.

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The most direct parallel to the Arafat case in U.S. history would be the exhumation of President Zachary Taylor that took place in 1991.
Taylor, the 12th president of the United States, died while in office, the second president to do so, and the cause of death was never established. Over 100 years after Taylor's death in 1850, one historian hypothesized that Taylor was assassinated by poison.
Forensic tests showed that Taylor wasn't poisoned after all, but likely died of cholera or severe gastroenteritis.

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A parking lot might seem like an odd final resting place for an English royal, but human remains found at a car park in Leicester may be King Richard III.
Richard III died in combat in 1485, and the skeletal remains found at the parking lot do show signs of battle trauma.
Results of DNA analysis following the exhumation are forthcoming.
MORE: Battle-Bruised Skeleton May Be Richard III

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The Danish astronomer Tycho Brahe died in 1601, yet his name made its way into the headlines recently after his remains were exhumed to clear up a 400-year-old mystery.
Brahe, the first astronomer in history to describe a supernova, died 11 days after the onset of a sudden illness despite a history of good health. One theory suggested that Brahe had in fact succumbed to mercury poisoning by his assistant, astronomer Johannes Kepler, or at the order of Danish king Christian IV, who was incensed that Brahe allegedly carried on an affair with the king's mother.
A team of forensic experts was able to disprove mercury poisoning as the cause of death, but couldn't conclusively determine what did take Brahe's life.
MORE: Danish Astronomer Not Poisoned

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One of the most famous cold cases in history was that of Anastasia Nikolaevna, daughter of tsar Nicholas II.
In 1918, Anastasia and the rest of her family were brutally assassinated at the height of the fever of revolution that turned Russia into a Communist state. For nearly 100 years after her death, however, rumors persisted that Anastasia had escaped the fate that had befallen the rest of her family. Several cases of Russian women claiming to be the princess emerged in the decades that followed.
The discovery of a mass grave in 1991 seemed to bolster the claim after the remains were identified as belonging to the tsar's family, with two of the children seemingly absent. In 2007, a grave in Yekaterinburg, Russia, was discovered and two years later proven to be the final resting place of the two young royals.
SEE ALSO: Royals Lost and Never Found

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Given that she's the subject of the most well-known portait in history, Lisa Gherardini might have a recognizable face, but her remains have proven trickier to identify.
In September, Italian researchers exhumed the remains of the woman believed to be Leonardo da Vinci's inspiration for Mona Lisa. Her final resting place is a grave beneath an altar at the Convent of St. Orsola.
Born in 1479, Gherardini was belonged to a noble family and married the wealthy merchant Francesco del Giocondo. She died in 1542, at age 63, according to church records.
Work at the site wrapped in October and results of DNA analysis are expected early next year.
SEE MORE: Mona Lisa Coming Back from the Grave?

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A nearly 400-year-old murder mystery involving the most powerful family of the Florentine Renaissance, the Medicis, was solved forensic anthropologists in 2010.
Francesco I de' Medici, Grand Duke of Tuscany, and his second wife, Bianca Cappello, died just hours apart following 11 days of agony from what was then a mysterious illness. His brother, Cardinal Ferdinando, depicted here, was suspected of orchestrating the deaths. Ferdinando had been at risk of being excluded from the succession and never accepted his brother's wife at court.
Analysis of the remains of the fallen Medicis, however, shows that malaria in fact was responsible for the deaths of Francesco and Bianca.
MORE: Medici Family Cold Case Finally Solved

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Ned Kelly might not be a household name in the United States. But in Australia, he has a reputation akin to American outlaw heroes like Billy the Kid.
Famous for robbing banks, holding up towns and engaging in shootouts with authorities, Kelly killed three police officers before the law caught up with him in 1880. Sentenced to hang, Kelly was executed that same year.
His body, however, was tossed into a mass grave an lost to history. A skull believed to belong to Kelly was stolen in 1978 but reemerged decades later, sparking an investigation into whether it was in fact Kelly.
DNA analysis verified that the remains did belong to Kelly after all.
MORE: Body of Infamous Aussie Outlaw Found

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Did former Chilean President Salvador Allende take his own life before troops stormed his presidential palace in 1973? Or did he die in a gun buttle, as some of his leftist supporters have suggested?
As the New York Times reports, a court order to exhume Allende's body last year answered that question once and for all. The forensic evidence, however, only led to further disputes.
The remains showed that two shots felled the former Chilean leader, one of which was fired by an assault rifle and the other possibly by a smaller gun. Although the official autopsy concludes that Allende died using the AK-47 given to him by Fidel Castro, conflicting determinations allege that Allende was assassinated and later shot again to make the death look like a suicide.

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Louis XVII, the last Dauphin of France before the title was restored after the French Revolution, never ascended to the throne. In 1793, his parents, King Louis XVI and Queen Marie Antoinette, were executed within a year after the eruption of revolution.
Even before his parents' death, Louis XVII had been held in prison. Two years after their executions, Louis XVII fell ill and died in prison. Similar to the stories that followed Anastasia's death, rumors abound that Louis XVII had not died, but rather escaped.
A DNA investigation carried out in 2000, however, on his remains proved that he had died in captivity as history records.
WATCH: Maggots? Flies? Corpses? All in a grisly day's work for a forensics expert.

In real life, it's more often the voice that offers the tell-tale evidence, since technology to recognize voices in recordings has become so much more sophisticated.

The Feb. 26 recording of a 911 call by a woman who reported someone crying out for help in her gated community in Sanford, Fla., could be a key piece of evidence in the Trayvon Martin murder case, especially since she called early enough so that screams for help and the gunshot were recorded.

George Zimmerman, a Neighborhood Watch volunteer, shot Martin, an unarmed 17-year-old. Why he did so remains a hotly argued topic, with Zimmerman claiming Martin attacked and beat him.

Tom Owen, a forensic consultant for Owen Forensic Services LLC and chair emeritus for the American Board of Recorded Evidence, recently analyzed the tape. After running the woman's 911 call through a software program called Easy Voice Biometrics and comparing it to another 911 call with Zimmerman's voice, Owen's team concluded that the screams for help were not Zimmerman's.

And, Owen said, if he had samples of Martin's voice, he may be able to definitively identify the screams as his.

"We've talked to the family; the attorney has been notified," he told Discovery News.

How can he be so sure?

Acoustic scientists have been using audio forensics since WWII when, with the aid of the newly invented sound spectrograph, they realized they might be able to identify enemy voices on radio broadcasts. The spectrograph graphed the frequency and amplitude of voice patterns.

The scientists realized the value of that information because, with the possible exception of twins, voiceprints are unique, forensic-audio examiner Stuart Allen told Discovery News.

"Unless you've had surgery, you can't disguise the characteristics of your vocal cords or mouth structure," he said.